Hearing aid apparatus



Dec. 11, 1956 H. E. CHRISTIANSEN 2,773,941

HEARING AID APPARATUS Filed July 15, 1952 3 Sheets-Sheet l Dec. 11, 1956 H. E. CHRISTIANSEN 2,773,941

' HEARING AID APPARATUS Filed July 15, 1952 5 Sheets-Sheet 5 INVFNTOR: 1620/ E. C'fi sf/aosen BY LAWN HEARING AID APPARATUS Henry E. Christiansen, Copenhagen, Denmark, assignor to American Danish Oticon Corporation, a corporation of Denmark Application July 15, 1952, Serial No. 298,909

Claims priority, appiication Denmark July 18, 1951 Claims. (Cl. 179-107) This invention relates to hearing aid apparatus and more specifically to bone conduction receivers of the electromagnetic type for converting electrical energy to vibrations to be transmitted to the bone structure of the user.

Bone conduction receivers may be divided into two general classes, direct acting and reaction. More specifically my invention relates to the reaction type of receiver in which the bone engaging contactor such as the exterior casing of the apparatus is supported by a head band or the like; the electromagnetic system hangs freely and inasmuch as this system has substantial mass it remains stationary while the contactor vibrates relatively thereto by reaction.

In bone conductors of the class here referred to one problem is to avoid unlineary distortion.

Another problem in connection with bone conductors of the class referred to is to avoid a resonance peak with in the audible range. A further problem is to avoid a decreased sensibility on either side of said resonance peak.

The Patent No. 2,522,099 to Demant discloses a bone conductor in which an armature member is fastened inside the exterior casing and connected with a resilient diaphragm supporting along its edge the electromagnetic system so as to form a substantial airtight interior space.

This structure aims to decrease the resonance peak, but it is not capable of amplifying the frequency range at either side of the resonance peak with the result that the sensibility of the bone conductor is not up to the standards of practical requirements.

It is one object of my invention to provide a hearing aid apparatus of the kind referred to which is more up to the standards of practical requirements than the prior devices known.

It is a further object of my invention to provide a device which has an improved utilization of the available small space.

It is a further object of my invention to provide a bone conductor enabling an improved yield in the electromagnetic system.

Still a further object of my invention is to provide a bone conductor having an improved frequency characteristic with a reduced non-linear distortion.

Still another object of my invention is to provide an apparatus of the kind referred to which enables a minimum of air gap between the energizing magnetic system and its armature.

Still another object resides in providing an apparatus 2,773,941 Patented Dec. 11, 1956 ported on a head band and connected in a microphone circuit,

Figure 2 is a longitudinal section through the receiver illustrating the interior construction thereof,

Figure 3 is a section along the line 33 in Figure 2,

Figure 4 is a section along the line 4-4 in Figure 2, and Figure 5 is a section along the line 55 in Figure 2.

Referring now to Figure 1 the bone conduction receiver includes a casing 10 of insulating material. As a suitable material for the-casing any convenient plastic or other mouldable material may be used. The casing comprises as more clearly shown in Figure 2 two portions, viz. a main portion 12 defining an interior cavity to receive the electromagnetic system and a cover portion 14 the exterior surface of which is preferably slightly curved so as to be better adapted to the ear bone structure of the user.

Extending from opposite sides of the casing portion 12 there is arranged a pair of pivot pins 16 and 18 to be received in bearings in a bifurcated portion 20 of the headband 22 which is of a convenient resilient material enabling the apparatus to be kept in position with the curved surface 24 of the cover 14 in engagement with the ear bone structure of the user.

The electrical means is energized by voice current picked up by a suitable microphone 26 in circuit with a battery or other sorts of power 28 and preferably a vacuum tube amplifier (not shown) connected to the electrical means within the casing by the flexible electric cord 30 having a separable plug type connector 32 plugged into the casing.

The vacuum tube amplifier does not form part of the present invention and further belongs to the general knowhow of those skilled in the art, so for these reasons it will not in the following be described in any detail.

The aforementioned electrical means within the casing is of the electromagnetic type and will be more detailed described with reference to Figures 25.

As mentioned hereinbefore my hearing aid apparatus is of the reaction type and comprises basicly an exterior casing referred to as 10, an armature member 40 secured to the casing and an electromagnetic system 42 resiliently supported by said armature in spaced relationship thereto.

As mentioned the casing comprises two parts 12 and 14. The part 12 is provided with a bottom 44 and a substantially annular wall 46 so as to define an interior cavity 48. As most clearly shown in Figures 2 and 3 the wall 46 is at opposite ends provided with portions having increased thickness. The left hand portion 50 is provided with a bushing 52 having interior screw threads adapted to receive a screw 54 serving the purpose of holding the cover 14 in position closing the cavity 48 and having its head counter-sunk in the surface of the cover.

The right hand end 56 is in a similar manner provided with a bushing 58 for receiving another screw 60 the head of which is also counter-sunk in the surface of the cover.

The end of the casing portion 56 is flattened at 62 and from the flattened surface there extend through the wall two bushings 64 and 66 adapted to receive the contact pins of the plug 32.

In the portion 56 of the casing there is provided a chamber 68 communicating with the interior cavity 52. From the chamber 68 there are extending in opposite direction notches 70 and 80. From the notch 70 there extend at the bottom oppositely directed notches 72 and 74 and in a similar manner there extend from the notch at the bottom-thereof oppositely directed notches 82 and 84. in either of these notches there are arranged contact members generally referred to as 'ltlfl'and respectively. With reference to Figures 2 and 3 the contact memher 100 comprises a strip like body portion 102 received in the notches 72 and 74. At the top end of the strip 102 there is provided a strip 104 extending inwardly in direction of the chamber 68 substantially vertical to the strip 102. The strip 104 is by means of a soldering or in any other convenient manner connected with an electric wire 120 leading to one end of the magnetic winding of the electromagnetic system. Spaced from the top strip 104 there is on the main strip member 102 provided another strip 106, for instance by stamping a part of the material of the strip 102 out of the plane and bending it inwardly as indicated most clearly in Figure 3 to such an extent that the surface of the strip 106 will form a resilient contact member cooperating with the plug pin introduced through the bushing 64.

In a similar manner the contact member 110 is provided with a main strip 112, a top soldering strip 114 connected with the other wire 122 and a resilient contact strip 116 adapted to cooperate with the other plug pin introduced through the bushing 66.

Preferably the interior cavity 48 is of circular cross section as shown in Figure 3 but may within the scope of the invention have any other convenient form. In order to center the cover 14 with respect to the casing portion 12 the cover may as shown in Figure 2 be provided with an annular shoulder 124 corresponding to the interior cross section of the cavity 48.

The electromagnetic system comprises a magnetic coil 130 which as mentioned by means of the wires 120 and 122 are connected with the terminals 100 and 110. The coil is arranged on a central core 132 and is surrounded by an annular magnetic member 134 which is connected with the core by means of a yoke 136 preferably of circular configuration and provided with a recess 138 for receiving the wires 120 and 122.

The exterior end of the annular magnet remote from the yoke is turned down to smaller diameter and shouldered at 140 to receive an exterior ring 142 in the surface of which there is provided a plurality of screw threaded holes 144, 146 and 148. In the present embodiment there are provided three holes, but it will be understood that any other convenient number of holes such as four, five or six may be used within the scope of the invention.

Spaced from the electromagnetic system here described by means of an air gap 150 there is provided the armature structure generally referred to as 40 and shown in detail in Figure 5. The armature comprises a central diskformed portion 152 preferably of circular configuration and having a central screw threaded hole 154 adapted to receive a screw 156 introduced through a central hole 158 in the bottom portion 44 of the casing so as to thereby secure the armature firmly to the casing. As shown the head of the screw 156 is preferably countersunk in the surface of the bottom. From the central armature portion 152 there are extending radial arms 160, 170 and 180, from the ends of which there are extending elongated arms 162, 172 and 182. More specifically the elongated arms 162, 172 and 182 are of arcuate configuration. As apparent from Figure either of said three arms forms an angle with radius through the center of the armature portions. Preferably the arcuate arms are extending substantially concentric with the periphery of the armature portion. As shown most clearly in Figure 2 the central armature portion 152 is thicker than the radial arms and the arcuate extensions thereof. example the arms and their arcuate extensions may be something like half the thickness of the central armature portion. It is important that the thickness of the arms and their arcuate extensions are so adapted to the material used for the armature structure that the arcuate extensions are resilient to a certain extent.

As material for the armature structure there is therefore preferably used an alloy of magnetizable material, which also has resilient qualifications. Such alloy will As an 4 easily be selected'between the known materials by those skilled in the art.

Adjacent the ends of the arcuate extensions 162, 172 and 182 there are provided holes 164, 174 and 184 for receiving screws 166, 176 and 186 by means of which the armature is connected with the electromagnetic structure by screwing the screws in the holes 144, 146 and 148. As apparent from the specification and the drawings either of the arms will provide a one-sided suspension of the magnetic system comprising the annular magnet 134, the center magnet 132, the yoke 136 and the magnetic coil 130.

Due to the fact that the direction of the arms differs from the direction of the radius, an improved frequency characteristic is obtained as will be further explained in connection with the operation of the bone conductor.

Between the armature and the electromagnetic structure there are provided distance washers 168, 178 and 188 so as to space the electromagnetic structure from the armature to form the air gap 150. Either the ring 142 or the screws 166, 176, 186 together with the washers 168, 178, 188 is of non-magnetizable material.

As it will be understood from this description the armature is firmly secured in the casing and supports resiliently the electromagnetic structure on the arms 162, 172, 182 only.

Hereby the mode of operation will be as follows:

When the magnet coil 130 is energized by sound current picked up by the microphone 26 and applied to the apparatus over the plug 32 and the terminals and 110, the magnetization of the system will be caused to vary in accordance with the sound waves. In view of the resiliency of the periphery portion of the armature structure allowing a resilient relative movement between the electromagnetic system and the armature the air gap will vary in accordance with the sound waves. As explained ,hereinbefore either of the three arms is to be considered stantial mass it will due to the inertia remain substantially stationary with the result that the variations of the air gap will cause the armature and the whole casing firmly secured thereon to vibrate in accordance with the sound waves so that the casing the arcuate surface 24 of which is held in contact with the ear bone of the user will transfer the vibrations to thebone structure with the result that the vibrations will be transferred to the ear and thereby made audible in form of sound waves.

Furthermore the specific support of the electromagnetic structure on the resilient periphery portion of the armature enables an improved parallelizing of the armature with the pole faces. Furthermore this improved parallelizing enables a smaller air gap to be used which also contributes to an improved efficiency of the apparatus. It will be understood that the embodiment of my apparatus hereinbefore described is only to beconsidered as an example. Such for instance the ring 142 may be omitted in which event the screws 166, 176 and 186 and the distance disks 168, 178 and 188 must be of non-magnetizable materiaL, As shown, however, the radial extension of the central armature portion is only slightly larger than the radial extension of the electromagnetic coil so as to concentrate the majority of the magnetic field on the central portion. As apparent from the drawing there is left outside the central armature portion only a relatively narrow annular surface of the annular magnet 134. This annular portion is further within the orbit of the ar'cua'te arms. Hereby the magnetic field is concentrated substantially in the airgap between the armature and the annular magnet without any substantial stray field.

I claim:

1. In a hearing aid apparatus of the reaction type in combination: an exterior casing defining a cavity, an armature having a substantially circular rigid armature portion firmly secured in the interior of said casing and a plurality of arms extending from said central armature portion, either of said arms having a resilient arcuate extension spaced from said central armature portion and substantially following the periphery thereof, an electromagnetic structure supported exclusively on said armature structure on spaced points adjacent the ends of either of said arcuate extensions in spaced relationship to said central armature portion and means for energizing said electromagnetic system by sound currents.

2. In a hearing aid apparatus of the reaction type in combination: an exterior casing defining a cavity, a rigid armature firmly secured in the interior of said casing, a plurality of resilient arms extending from said armature, either of said arms following substantially the periphery of said armature in spaced relationship thereto, an electromagnetic structure supported exclusively on said arms adjacent the free ends thereof in spaced relationship to said armature and means for energizing said electromagnetic system by sound currents.

3. In a hearing aid apparatus of the reaction type in combination: a vibration responsive plate having a surface adapted to engage the body of the user, electromagnetic means comprising an energizable magnet and an armature spaced from said magnet by means of an air gap, said armature having a rigid central portion and a plurality of resilient arms extending therefrom either of said arms forming an angle with radius through the center of said central armature portion, means for energizing said electromagnetic means for varying said air gap responsive to sound currents, a direct connection between said rigid central armature portion and said vibration plate and means for supporting said energizable magnet adjacent the ends of either of said resilient arms only.

4. In a hearing aid apparatus of the reaction type in combination: a vibration responsive plate having a surface adapted to engage the body of the user, electromagnetic means comprising an energizable magnet and an armature spaced from said magnet by means of an air gap and being substantially concentric, said armature having a rigid central portion and a plurality of resilient arms substantially concentric therewith, means for energizing said electromagnetic means to vary said air gap responsive to sound currents, a rigid connection between said central armature portion and said vibration plate and a connection between the ends only of said resilient arms and said energizable magnet.

5. In a hearing aid apparatus of the reaction type in combination: a vibration responsive member having a surface adapted to engage the body of the user, electromagnetic means comprising a magnetic system including a center core, an annular magnet surrounding said center core, a ma netic yoke connecting said center core and said annular magnet and an energizer coil for said magnetic system and an annular armature spaced from said magnetic system by means of an air gap, said armature and said magnetic system being substantially concentric, an exterior ring surrounding said annular magnet, a plurality of resilient arms extending from said armature substantially concentric therewith, a rigid connection between said armature and said vibration member and a connection between the end only of either of said resilient arms and said ring that surrounds said annular magnet so as to resiliently support said magnetic system on said arms spaced from each other by said air gap.

6. In a hearing aid apparatus of the reaction type in combination: an exterior casing defining a cavity and having a surface adapted to engage the body of the user, an electromagnetic structure comprising an annular armature and an energizable annular electromagnetic structure spaced from one another by an air gap, said armature being rigidly connected with said casing in the interior thereof, said armature further having three resilient arms, means for supporting said electromagnet on the ends only of either of said resilient arms only, and means for energizing said electromagnetic structure by sound currents.

7. in a reaction type hearing aid apparatus having a vibration member adapted to be held in contact with the bone of the user, an armature firmly secured to said vibration member, a plurality of arms firmly secured to said armature, either of said arms having a radial portion and a non-radial extension having a free end, a magnetic system supported on the free ends only of said extending arms in a position spaced from said armature with an air gap and means for energizing said magnetic system with currents of sound frequency.

8. In a reaction type hearing aid apparatus having a vibration member adapted to be held in contact with the bone structure of the user, an armature firmly secured to said vibration member, a plurality of arms firmly secured to said armature and extending from the periphery thereof, either of said arms having a portion extending freely at an angle with respect to radius through the center of said armature and having a free end, a magnetic system supported on the free ends of said extending arm portions in a position spaced from said armatu-reby an air gap and means for energizing said magnetic system with current of sound frequency.

9. In a reaction type hearing aid apparatus of the bone conduction type including a driving structure and having a vibration member adapted to be held in contact with the bone structure of the user, said driving structure including an energiza-ble electromagnetic structure comprising an electromagnetic system for producing an electromagnetic field and an armature spaced from said electromagnetic structure by means of an air gap, said armature being rigidly secured to said vibration member, said armature having resilient arms extending outside its periphery, either of said resilient arms being located substantially in the plane of said armature and being inclined with respect to the periphery thereof, a rigid supporting connection between said electromagnetic structure and said arms at the ends thereof only and means for energizing said electromagnetic system with currents of sound frequency.

10. In and for a hearing aid apparatus of the reaction type comprising a vibration responsive member adapted to engage the bone structure of the user and an electromagnetic system adapted to be energized by currents of sound frequency and resiliently connected with said vibration responsive member, an armature structure comprising an armature portion for said electromagnetic structure and a plurality of resilient arms extending substantially in the plane of said armature portion outside the periphery thereof in inclined relationship with respect to said periphery and means connecting the end only of either of said resilient arm with said electromagnetic structure in a relative position of said electro magnetic structure and said armature portion defining therebetween an air gap.

References Cited in the file of this patent UNITED STATES PATENTS 2,165,710 Koch July 11, 1939 2,459,325 Knowles Jan. 18, 1949 2,482,044 Vernier Sept. 13, 1949 2,500,541 Greibach Mar. 14, 1950 2,680,157 Wolfi June 1, 1954 

